In the optical device field, the hermetic sealing structure and hermetic sealing method of each optical device are important technologies to attain the long-term reliability of the optical device, and also in an optical waveguide wavelength conversion device, the hermetic sealing structure has become a very important factor, since it is necessary to protect against external humidity and dust for stabilization of the characteristic of an optical waveguide itself, stabilization of the characteristic of an optical semiconductor, such as a semiconductor laser, and attainment of long-term reliability.
In a hermetic sealing method in a conventional optical device, when a metallic package or a ceramic package is used in general, seam welding, such as resistance welding, can be applied between the main body of the package and the lid. For example, in the hermetic sealing method of an optical semiconductor module, as disclosed in Japanese Laid-open Patent Application No. Hei 6-82660, the module is configured so as to be hermetically sealed by seam-welding or soldering the upper face of the main body and the lid. By this seam-welding and soldering, sufficient hermeticity can be maintained inside the package. However, when it is considered that a light-emitting device, such as a semiconductor laser, is mounted on an optical pickup, it is important to reduce the weight and cost of the package itself; since the package formed of a resin, such as plastic, is lightweight and inexpensive, the resin is one of promising package materials. In the case when a resin package is used, a package sealing method using an adhesive, instead of the seam-welding or soldering, is most effective.
In the case when an adhesive is used for a method of sealing a package including a semiconductor laser and an optical waveguide wavelength conversion device that makes the wavelength of the light of the semiconductor laser short, in a conventional hermetically-sealing structure shown in FIG. 13, a lid portion securing agent 1302 on the A-face 1308 of FIG. 13 makes contact with gas hermetically sealed inside the package, whereby unnecessary gas 1306 evolved from the adhesive or unnecessary gas 1306 generated from the adhesive at the time of curing is mixed inside the package. In addition, an adhesive is used to secure an optical waveguide wavelength conversion device 1304 and a sub-mount 1305 inside the package, whereby unnecessary gas 1307 from the adhesive is also mixed inside the package just as in the case of securing the lid.
Conventionally, in the case of an incoherent incandescent lamp, a light-emitting diode, a long-wavelength semiconductor laser or the like, large energy is not concentrated near its light-emitting point, whereby the light-emitting point is not affected adversely. However, short-wavelength light emitted from a short-wavelength semiconductor laser, such as a blue laser, or an optical waveguide, is coherent light, and large energy of 10 kW/cm2 or more is concentrated near the end face of the laser chip or the light-emitting point of the optical waveguide; therefore, the particles of the unnecessary gas are attracted thereto, and the unnecessary gas present inside the package are deposited on the end face of the chip or the end face of the optical waveguide, that is, the light emission portions, thereby causing the problem of lowering the optical output.
In addition, in the case when an ultraviolet curing resin is used as a package sealing and securing agent and an optical waveguide wavelength conversion device securing agent, bluish violet light or ultraviolet light emitted from the semiconductor laser or the optical waveguide reacts with outside gas, that is, unnecessary caused by the ultraviolet curing resin present in the atmosphere inside the package, and the unnecessary gas is further deposited significantly on the end face of the optical waveguide, thereby causing the problem of losing long-term reliability.
Furthermore, in the case when the optical waveguide wavelength conversion device is turned on continuously in the air atmosphere without being secured to the inside of the package, large energy is concentrated to the end face of the optical waveguide; therefore, foreign particles, such as dust, dirt and carbide, present in the air, are deposited on the end face of the blue light emission portion, thereby causing the problem of lowering the output of the blue light, deteriorating the transverse mode and losing the long-term reliability.